Sensor device including one or more metal-dielectric optical filters

ABSTRACT

A sensor device including one or more sensor elements and one or more optical filters is provided. The one or more optical filters each include a plurality of dielectric layers and a plurality of metal layers stacked in alternation. The metal layers are intrinsically protected by the dielectric layers. In particular, the metal layers have tapered edges that are protectively covered by one or more of the dielectric layers.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/720,728, filed Dec. 19, 2012 (now U.S. Pat. No. 9,448,346), thecontent of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a sensor device including one or moreoptical filters, more particularly, one or more metal-dielectric opticalfilters.

BACKGROUND OF THE INVENTION

Image sensors are sensor devices that are used in imaging devices, suchas cameras, scanners, and copiers, to convert optical signals intoelectrical signals, allowing image capture. An image sensor, generally,includes a plurality of sensor elements and a plurality of opticalfilters disposed over the plurality of sensor elements. A color imagesensor includes a plurality of color filters disposed in an array, i.e.,a color filter array (CFA). The CFA includes different types of colorfilters having different color passbands, e.g., red, green, and blue(RGB) filters.

Conventionally, absorption filters formed using dyes are used as colorfilters. Unfortunately, such dye-based color filters have relativelybroad color passbands, resulting in less brilliant colors.Alternatively, dichroic filters, i.e., interference filters, formed ofstacked dielectric layers may be used as color filters. Suchall-dielectric color filters have higher transmission levels andnarrower color passbands, resulting in brighter and more brilliantcolors. However, the color passbands of all-dielectric color filtersundergo relatively large center-wavelength shifts with changes inincidence angle, resulting in undesirable shifts in color.

Furthermore, all-dielectric color filters, typically, include a largenumber of stacked dielectric layers and are relatively thick.Consequently, all-dielectric color filters are expensive and difficultto manufacture. In particular, all-dielectric color filters aredifficult to etch chemically. Lift-off processes are, therefore,preferred for patterning. Examples of lift-off processes for patterningall-dielectric CFAs are disclosed in U.S. Pat. No. 5,120,622 toHanrahan, issued on Jun. 9, 1992, in U.S. Pat. No. 5,711,889 toBuchsbaum, issued on Jan. 27, 1998, in U.S. Pat. No. 6,238,583 toEdlinger, et al., issued on May 29, 2001, in U.S. Pat. No. 6,638,668 toBuchsbaum, et al., issued on Oct. 28, 2003, and in U.S. Pat. No.7,648,808 to Buchsbaum, et al., issued on Jan. 19, 2010, which areincorporated herein by reference. However, lift-off processes are,generally, limited to a filter spacing of about twice the filter height,which makes it difficult to achieve all-dielectric CFAs suitable forsmaller color image sensors.

In addition to transmitting visible light in color passbands, bothdye-based and all-dielectric color filters also transmit infrared (IR)light, which contributes to noise. Therefore, a color image sensor,typically, also includes an IR-blocking filter disposed over the CFA.Conventionally, absorption filters formed of colored glass or dichroicfilters formed of stacked dielectric layers are used as IR-blockingfilters. Alternatively, induced transmission filters formed of stackedmetal and dielectric layers may be used as IR-blocking filters. Examplesof metal-dielectric IR-blocking filters are disclosed in U.S. Pat. No.5,648,653 to Sakamoto, et al., issued on Jul. 15, 1997, and in U.S. Pat.No. 7,133,197 to Ockenfuss, et al., issued on Nov. 7, 2006, which areincorporated herein by reference.

To avoid the use of an IR-blocking filter, induced transmission filtersformed of stacked metal and dielectric layers may be used as colorfilters. Such metal-dielectric color filters are inherently IR-blocking.Typically, metal-dielectric color filters have relatively narrow colorpassbands that do not shift significantly in wavelength with changes inincidence angle. Furthermore, metal-dielectric color filters are,generally, much thinner than all-dielectric color filters. Examples ofmetal-dielectric color filters are disclosed in U.S. Pat. No. 4,979,803to McGuckin, et al., issued on Dec. 25, 1990, in U.S. Pat. No. 6,031,653to Wang, issued on Feb. 29, 2000, in U.S. Patent Application No.2009/0302407 to Gidon, et al., published on Dec. 10, 2009, in U.S.Patent Application No. 2011/0204463 to Grand, published on Aug. 25,2011, and in U.S. Patent Application No. 2012/0085944 to Gidon, et al.,published on Apr. 12, 2012, which are incorporated herein by reference.

Typically, the metal layers in metal-dielectric color filters are silverlayers, which are environmentally unstable and which deteriorate whenexposed to even small amounts of water or sulfur. Chemically etching thesilver layers exposes the edges of the silver layers to the environment,allowing deterioration. Therefore, in most instances, metal-dielectricCFAs are patterned by adjusting the thicknesses of only the dielectriclayers to select different color passbands for the metal-dielectriccolor filters. In other words, different types of metal-dielectric colorfilters having different color passbands are required to have the samenumber of silver layers as one another and the same thicknesses of thesilver layers as one another. Unfortunately, these requirements severelylimit the possible optical designs for the metal-dielectric colorfilters.

The present invention provides metal-dielectric optical filters that arenot subject to these requirements, which are particularly suitable foruse in image sensors and other sensor devices.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a sensor devicecomprising: one or more sensor elements; and one or more optical filtersdisposed over the one or more sensor elements, wherein each of the oneor more optical filters includes: a plurality of dielectric layers; anda plurality of metal layers stacked in alternation with the plurality ofdielectric layers, wherein each of the plurality of metal layers has atapered edge, at a periphery of the optical filter, that is protectivelycovered by one or more of the plurality of dielectric layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail with referenceto the accompanying drawings wherein:

FIG. 1A is a schematic illustration of a cross-section of a firstembodiment of an optical filter;

FIGS. 1B to 1G are schematic illustrations of steps in a method offabricating the optical filter of FIG. 1A;

FIG. 2 is a schematic illustration of a cross-section of a secondembodiment of an optical filter;

FIG. 3 is a schematic illustration of a cross-section of a plurality ofoptical filters;

FIG. 4A is a table of layer numbers, materials, and thicknesses for anexemplary red filter;

FIG. 4B is a table of layer numbers, materials, and thicknesses for anexemplary green filter;

FIG. 4C is a table of layer numbers, materials, and thicknesses for anexemplary blue filter;

FIG. 4D is a table of layer numbers, materials, and thicknesses for anexemplary photopic filter;

FIGS. 5A and 5B are plots of transmission spectra for the exemplary red,green, and blue filters of FIGS. 4A to 4C;

FIG. 5C is a plot of transmission spectra at incidence angles of 0° to60° for the exemplary photopic filter of FIG. 4D;

FIG. 6A is a plot of color gamuts for the exemplary red, green, and blue(RGB) filter set of FIGS. 4A to 4C and for a conventional dye-based RGBfilter set;

FIG. 6B is a plot of color trajectories at incidence angles of 0° to 60°for the exemplary red filter of FIG. 4A and for a conventionalall-dielectric red filter;

FIG. 6C is a plot of a color trajectory at incidence angles of 0° to 60°for the exemplary photopic filter of FIG. 4D;

FIG. 7 is a schematic illustration of a cross-section of a firstembodiment of a sensor device; and

FIG. 8 is a schematic illustration of a cross-section of a secondembodiment of a sensor device.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a metal-dielectric optical filter havingprotected metal layers, which is particularly suitable for use in asensor device. The optical filter includes a plurality of dielectriclayers and a plurality of metal layers stacked in alternation. The metallayers are intrinsically protected by the dielectric layers. Inparticular, the metal layers have tapered edges that are protectivelycovered by one or more of the dielectric layers. Accordingly, the metallayers have increased resistance to environmental degradation, resultingin a more durable optical filter.

In some embodiments, the dielectric layers and the metal layers arestacked without any intervening layers. With reference to FIG. 1A, afirst embodiment of the optical filter 100, disposed on a substrate 110,includes three dielectric layers 120 and two metal layers 130 stacked inalternation. The metal layers 130 are each disposed between and adjacentto two dielectric layers 120 and are, thereby, protected from theenvironment.

The metal layers 130 have tapered edges 131 at a periphery 101 of theoptical filter 100. In other words, the metal layers 130 aresubstantially uniform in thickness throughout a central portion 102 ofthe optical filter 100, but taper off in thickness at the periphery 101of the optical filter 100. Likewise, the dielectric layers 120 aresubstantially uniform in thickness throughout the central portion 102 ofthe optical filter 100, but taper off in thickness at the periphery 101of the optical filter 100. Accordingly, the central portion 102 of theoptical filter 100 is substantially uniform in height, whereas theperiphery 101 of the optical filter 100 is sloped. In other words, theoptical filter 100 has a substantially flat top and sloped sides.

Advantageously, the tapered edges 131 of the metal layers 130 are notexposed to the environment. Rather, the tapered edges 131 of the metallayers 130 are covered by one or more of the dielectric layers 120. Theone or more dielectric layers 120 suppress environmental degradation,e.g., corrosion, of the metal layers 130, e.g., by inhibiting thediffusion of sulfur and water into the metal layers 130. Preferably, themetal layers 130 are substantially encapsulated by the dielectric layers120. More preferably, the tapered edges 131 of the metal layers 130 areprotectively covered by adjacent dielectric layers 120, and the metallayers 130 are substantially encapsulated by adjacent dielectric layers120.

With reference to FIGS. 1B to 1G, the first embodiment of the opticalfilter 100 may be fabricated by a lift-off process. With particularreference to FIG. 1B, in a first step, the substrate 110 is provided.With particular reference to FIG. 1C, in a second step, a photoresistlayer 140 is applied onto the substrate 110. Typically, the photoresistlayer 140 is applied by spin coating or spray coating.

With particular reference to FIG. 1D, in a third step, the photoresistlayer 140 is patterned to uncover a region of the substrate 110 wherethe optical filter 100 is to be disposed, i.e., a filter region. Otherregions of the substrate 110 remain covered by the patterned photoresistlayer 140. Typically, the photoresist layer 140 is patterned by firstexposing a region of the photoresist layer 140 covering the filterregion of the substrate 110 to ultraviolet (UV) light through a mask,and then developing, i.e., etching, the exposed region of thephotoresist layer 140 by using a suitable developer or solvent.

The photoresist layer 140 is patterned in such a manner that an overhang141, i.e., an undercut, is formed in the patterned photoresist layer 140surrounding the filter region. Typically, the overhang 141 is formed bychemically modifying, e.g., by using a suitable solvent, a top portionof the photoresist layer 140, so that the top portion develops moreslowly than a bottom portion of the photoresist layer 140.Alternatively, the overhang 141 may be formed by applying a dual-layerphotoresist layer 140, consisting of a top layer that develops moreslowly and a bottom layer that develops more quickly, to the substrate110.

With particular reference to FIG. 1E, in a fourth step, a multilayerstack 103 is deposited onto the patterned photoresist layer 140 and thefilter region of the substrate 110. A portion of the multilayer stack103 disposed on the filter region of the substrate 110 forms the opticalfilter 100. The layers of the multilayer stack 103, which correspond tothe layers of the optical filter 100, may be deposited by using avariety of deposition techniques, such as: evaporation, e.g., thermalevaporation, electron-beam evaporation, plasma-assisted evaporation, orreactive-ion evaporation; sputtering, e.g., magnetron sputtering,reactive sputtering, alternating-current (AC) sputtering, direct-current(DC) sputtering, pulsed DC sputtering, or ion-beam sputtering; chemicalvapor deposition, e.g., plasma-enhanced chemical vapor deposition; andatomic layer deposition. Moreover, different layers may be deposited byusing different deposition techniques. For example, the metal layers 130may be deposited by sputtering of a metal target, and the dielectriclayers 120 may be deposited by reactive sputtering of a metal target inthe presence of oxygen.

Because the overhang 141 shadows a periphery of the filter region of thesubstrate 110, the deposited layers taper off in thickness towards theperiphery 101 of the optical filter 100. When a dielectric layer 120 isdeposited onto a metal layer 130, the dielectric layer 120 covers notonly the top surface of the metal layer 130, but also the tapered edges131 of the metal layer 130, thereby, protecting the metal layer 130 fromthe environment.

With particular reference to FIG. 1F, in a fifth step, a portion of themultilayer stack 103 on the patterned photoresist layer 140 is removed,i.e., lifted off, together with the photoresist layer 140. Typically,the photoresist layer 140 is stripped by using a suitable stripper orsolvent. The optical filter 100 remains on the filter region of thesubstrate 110. The substrate 110 may, for example, be a conventionalsensor element.

It should be noted that the lift-off process of FIGS. 1B to 1F may alsobe used to simultaneously form a plurality of optical filters 100 of thesame type, i.e., having the same optical design, on the substrate 110.Moreover, the lift-off process may be repeated to subsequently form oneor more optical filters of a different type, i.e., having a differentoptical design, on the same substrate 110. Thereby, an optical filterarray may be formed on the substrate 110. The substrate 110 may, forexample, be a conventional sensor array.

With reference to FIG. 1G, in an optional sixth step, an additionaldielectric coating 150 is deposited onto the optical filter 100. Thedielectric coating 150 may be deposited by using one of the depositiontechniques mentioned heretofore. The dielectric coating 150 covers boththe central portion 102 and the periphery 101 of the optical filter 100,i.e., all exposed portions of the optical filter 100, thereby,protecting the optical filter 100 from the environment.

In other embodiments, the optical filter includes a plurality ofcorrosion-suppressing layers, disposed between the dielectric layers andthe metal layers, which further protect the metal layers. With referenceto FIG. 2, a second embodiment of the optical filter 200, disposed on asubstrate 210, is similar to the first embodiment of the optical filter100, but further includes four corrosion-suppressing layers 260 insertedbetween the three dielectric layers 220 and the two metal layers 230.

The metal layers 230 are each disposed between and adjacent to twocorrosion-suppressing layers 260 and are, thereby, further protectedfrom the environment. The corrosion-suppressing layers 260 suppresscorrosion of the metal layers 230, principally during the depositionprocess. In particular, the corrosion-suppressing layers 260 protectportions of the metal layers 230 in the optical path, inhibitingdegradation of the optical properties of the metal layers 230.Preferably, tapered edges 231 of the metal layers 230 are protectivelycovered by adjacent corrosion-suppressing layers 260, as well as bynearest dielectric layers 220. Thus, the metal layers 230 are,preferably, substantially encapsulated by adjacent corrosion-suppressinglayers 260, as well as by nearest dielectric layers 220.

The second embodiment of the optical filter 200 may be fabricated by alift-off process similar to that used to fabricate the first embodimentof the optical filter 100. However, the layers of the multilayer stackdeposited in the fourth step correspond to the layers of the opticalfilter 200. In particular, corrosion-suppressing layers 260 aredeposited before and after each metal layer 230. Advantageously, thecorrosion-suppressing layers 260 suppress corrosion, i.e., oxidation, ofthe metal layers 230 during deposition of the dielectric layers 220.

The corrosion-suppressing layers 260 may be deposited as metal compound,e.g., metal nitride or metal oxide, layers by using one of thedeposition techniques mentioned heretofore. Alternatively, thecorrosion-suppressing layers 260 may be formed by first depositingsuitable metal layers, by using one of the deposition techniquesmentioned heretofore, and subsequently oxidizing the metal layers.Preferably, the corrosion-suppressing layers 260 are each formed byfirst depositing a suitable metal layer, oxidizing the metal layer, andthen depositing a metal oxide layer. For example, thecorrosion-suppressing layers 260 may be formed by sputtering of asuitable metal target followed by oxidation, followed by reactivesputtering of a suitable metal target in the presence of oxygen. Furtherdetails of methods of forming corrosion-suppressing layers are disclosedin U.S. Pat. No. 7,133,197.

The optical filter of the present invention may have a variety ofoptical designs. The optical designs of exemplary optical filters willbe described in further detail hereafter. In general, the optical designof the optical filter is optimized for a particular passband byselecting suitable layer numbers, materials, and/or thicknesses.

Typically, the optical filter includes 2 to 6 metal layers, 3 to 7dielectric layers, and, optionally, 4 to 12 corrosion-suppressinglayers. In general, increasing the number of metal layers provides apassband with steeper edges, but with a lower in-band transmittance.

The first layer in the optical design, i.e., the first layer depositedon the substrate, may be a metal layer or a dielectric layer. The lastlayer in the optical design, i.e., the last layer deposited on thesubstrate, is usually a dielectric layer. When the first layer is ametal layer, the optical filter may consist of n metal layers (M) and ndielectric layers (D) stacked in a sequence of (M/D)_(n), where n≥2.Alternatively, the optical filter may consist of n metal layers (M), ndielectric layers (D), and 2n corrosion-suppressing layers (C), stackedin a sequence of (C/M/C/D)_(n), where n≥2. When the first layer is adielectric layer, the optical filter may consist of n metal layers (M)and n+1 dielectric layers (D) stacked in a sequence of D(M/D)_(n), wheren≥2. Alternatively, the optical filter may consist of n metal layers(M), n+1 dielectric layers (D), and 2n corrosion-suppressing layers (C),stacked in a sequence of D(C/M/C/D)_(n), where n≥2.

The metal layers are each composed of a metal or alloy. Typically, themetal layers are each composed of silver. Alternatively, the metallayers may each be composed of a silver alloy. For example, a silveralloy consisting essentially of about 0.5 wt % gold, about 0.5 wt % tin,and a balance of silver may provide improved corrosion resistance.Generally, but not necessarily, the metal layers are composed of thesame metal or alloy, but have different thicknesses. Typically, themetal layers each have a physical thickness between about 5 nm and about50 nm, preferably, between about 10 nm and about 35 nm.

The dielectric layers are each composed of a dielectric material.Typically, the dielectric layers are each composed of a high-indexdielectric material, i.e., a dielectric material having a refractiveindex greater than about 1.65 at 550 nm, that is transparent in thevisible spectral region. Suitable examples of high-index dielectricmaterials include titanium dioxide (TiO₂), zirconium dioxide (ZrO₂),niobium pentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅), and mixturesthereof. Preferably, the high-index dielectric material is alsoUV-absorbing, i.e., absorbing in the near-UV spectral region. Forexample, a high-index dielectric material including or consisting ofTiO₂ and/or Nb₂O₅ may provide enhanced UV blocking, i.e., lowerout-of-band transmittance in the near-UV spectral region. Preferably,the high-index dielectric material has a refractive index greater thanabout 2.0 at 550 nm, more preferably, greater than about 2.35 at 550 nm.A higher refractive index is usually desirable. However, the transparenthigh-index dielectric materials that are currently available, generally,have refractive indices less than about 2.7 at 550 nm.

Generally, but not necessarily, the dielectric layers are composed ofthe same dielectric material, but have different thicknesses. Typically,the dielectric layers each have a physical thickness between about 20 nmand about 300 nm. This physical thickness is selected to correspond witha quarter wave optical thickness (QWOT) required by an optical design.The QWOT is defined as 4nt, where n is the refractive index of thedielectric material and t is the physical thickness. Typically, thedielectric layers each have a QWOT between about 200 nm and about 2400nm.

The optional corrosion-suppressing layers are each composed of acorrosion-suppressing material. Typically, the corrosion-suppressinglayers are composed of a corrosion-suppressing dielectric material.Examples of suitable corrosion-suppressing dielectric materials includesilicon nitride (Si₃N₄), TiO₂, Nb₂O₅, zinc oxide (ZnO), and mixturesthereof. Preferably, the corrosion-suppressing dielectric material is acompound, e.g., a nitride or an oxide, of a metal having a highergalvanic potential than the metal or alloy of the metal layers.

The corrosion-suppressing layers are, generally, suitably thin tosubstantially avoid contributing to the optical design of the opticalfilter, especially when they are absorbing in the visible spectralregion. Typically, the corrosion-suppressing layers each have a physicalthickness between about 0.1 nm and about 10 nm, preferably, betweenabout 1 nm and about 5 nm. Further details of suitablecorrosion-suppressing layers are disclosed in U.S. Pat. No. 7,133,197.

The optional dielectric coating is composed of a dielectric material.The dielectric coating may be composed of the same dielectric materialsand may have the same range of thicknesses as the dielectric layers.Typically, the dielectric coating is composed of the same dielectricmaterial as the last dielectric layer and has a thickness that is aportion of the design thickness, i.e., the thickness required by theoptical design, of the last dielectric layer. In other words, the lastdielectric layer of the optical design is split between a dielectriclayer and a dielectric coating. For example, if the last dielectriclayer has a design thickness t_(d) and the dielectric coating has acoating thickness t_(c), e.g., 250 QWOT, the actual thickness t_(a) ofthe last dielectric layer is given by: t_(a)=t_(d)−t_(c).

With reference to FIG. 3, the optical filter 300, typically, has afilter height h, i.e., a height of the central portion of the opticalfilter 300 from the substrate 310, of less than 1 μm, preferably, ofless than 0.6 μm. Also typically, the optical filter 300 has a filterwidth w, i.e., a width of the central portion of the optical filter 300,of less than 2 μm, preferably, of less than 1 μm. Advantageously, therelatively small filter height allows a smaller filter spacing when aplurality of optical filters 300 are formed by a lift-off process.Typically, the optical filters 300 have a filter spacing d, i.e., aspacing between the central portions of nearest optical filters 300, ofless than 2 μm, preferably, of less than 1 μm.

The optical filter is a metal-dielectric bandpass filter, i.e., aninduced transmission filter, having a high in-band transmittance and alow out-of-band transmittance. Typically, the optical filter has amaximum in-band transmittance of greater than about 50%, an averageout-of-band transmittance of less than about 2% between about 300 nm andabout 400 nm, i.e., in the near-UV spectral region, and an averageout-of-band transmittance of less than about 0.3% between about 750 nmand about 1100 nm, i.e., in the infrared (IR) spectral region.Generally, the optical filter also has a low angle shift, i.e.,center-wavelength shift with change in incidence angle from 0°.Typically, the optical filter has an angle shift at an incidence angleof 60° of less than about 5% or about 30 nm in magnitude for an opticalfilter centered at 600 nm.

In some embodiments, the optical filter is a color filter having arelatively narrow color passband in the visible spectral region. Forexample, the optical filter may be a red, green, blue, cyan, yellow, ormagenta filter. In other embodiments, the optical filter is a photopicfilter having a photopic passband, i.e., a passband that mimics thespectral response of the human eye to relatively bright light, in thevisible spectral region. In yet other embodiments, the optical filter isan IR-blocking filter having a relatively broad passband in the visiblespectral region.

Optical designs, i.e., layer numbers, materials, and thicknesses, forexemplary red, green, and blue filters, i.e., an exemplary RGB filterset, are tabulated in FIGS. 4A, 4B, and 4C, respectively. An opticaldesign for an exemplary photopic filter is tabulated in FIG. 4D. Thelayers of each optical design are numbered starting from the first layerdeposited on the substrate.

The metal layers are each composed of silver, and have physicalthicknesses between about 13 nm and about 34 nm. The dielectric layersare each composed of a high-index dielectric material (H), and haveQWOTs between about 240 nm and about 2090 nm. For example, thehigh-index dielectric material may be a mixture of Nb₂O₅ and TiO₂ havinga refractive index of about 2.43 at 550 nm. The corrosion-suppressinglayers are each composed of ZnO and each have a physical thickness ofabout 2 nm.

When the high-index dielectric material has a refractive index of about2.43 at 550 nm, the filter height of the red filter is 606 nm, that ofthe green filter is 531 nm, that of the blue filter is 252 nm, and thatof the photopic filter is 522 nm. These filter heights are considerablysmaller than those of conventional all-dielectric optical filters.

Transmission spectra 570, 571, and 572 for the exemplary red, green, andblue filters are plotted in FIGS. 5A and 5B. The transmission spectrum570 for the exemplary red filter includes a red passband centered atabout 620 nm, the transmission spectrum 571 for the exemplary greenfilter includes a green passband centered at about 530 nm, and thetransmission spectrum 572 for the exemplary blue filter includes a bluepassband centered at about 445 nm.

Transmission spectra 573 and 574 for the exemplary photopic filter atincidence angles of 0° to 60° are plotted in FIG. 5C. The transmissionspectrum 573 for the exemplary photopic filter at an incidence angle of0° includes a photopic passband centered at about 555 nm. In thetransmission spectrum 574 for the exemplary photopic filter at anincidence angle of 60°, the photopic passband is centered at about 520nm. In other words, the angle shift of the exemplary photopic filter atan incidence angle of 60° is about −25 nm.

The exemplary optical filters each have a maximum in-band transmittanceof greater than about 60%. Advantageously, the exemplary optical filtersprovide improved IR blocking relative to conventional dye-based andall-dielectric optical filters, reducing noise caused by IR leaking.Specifically, the exemplary optical filters each have an averageout-of-band transmittance of less than about 0.3% between about 750 nmand about 1100 nm, i.e., in the IR spectral region. The exemplaryoptical filters, particularly the exemplary red filter, also provideimproved UV blocking relative to some conventional metal-dielectriccolor filters, reducing noise caused by UV leaking Specifically, theexemplary optical filters each have an average out-of-band transmittanceof less than about 2% between about 300 nm and about 400 nm, i.e., inthe near-UV spectral region.

A color gamut 680 for the exemplary RGB filter set is plotted on a CIExy chromaticity diagram in FIG. 6A, along with a color gamut 681 for aconventional dye-based RGB filter set for comparison. Advantageously,the color gamut 680 of the exemplary RGB filter set is considerablylarger than the color gamut 681 of the conventional dye-based RGB filterset.

A color trajectory 682 for the exemplary red filter at incidence anglesof 0° to 60° is plotted on a CIE xy chromaticity diagram in FIG. 6B,along with a color trajectory 683 for a conventional all-dielectric redfilter at incidence angles of 0° to 60°. A color trajectory 684 for theexemplary photopic filter at incidence angles of 0° to 60° is plotted ona CIE xy chromaticity diagram in FIG. 6C. Advantageously, the angleshift of the exemplary optical filters is considerably smaller than theangle shift of conventional all-dielectric optical filters.

The optical filter of the present invention is particularly useful whenincluded as part of a sensor device. The sensor device may be any typeof sensor device including one or more sensor elements, in addition toone or more of the optical filters of the present invention. Forexample, the sensor device may be an ambient light sensor, a proximitysensor, or an image sensor. The one or more sensor elements may be anytype of conventional sensor elements. Typically, the one or more sensorelements are photodetectors, such as photodiodes, charge-coupled device(CCD) sensor elements, or complementary metal-oxide semiconductor (CMOS)sensor elements. The one or more sensor elements may be front- orback-illuminated.

The one or more optical filters are disposed over the one or more sensorelements, so that the one or more optical filters filter light providedto the one or more sensor elements. Typically, each optical filter isdisposed over one sensor element. In other words, each pixel of thesensor device, typically, includes one optical filter and one sensorelement. Preferably, the one or more optical filters are disposeddirectly on the one or more sensor elements. For example, the one ormore optical filters may be formed on the one or more sensor elements bya lift-off process. However, in some instances, there may be one or morecoatings disposed between the one or more optical filters and the one ormore sensor elements.

In some embodiments, the sensor device includes a single sensor elementand a single optical filter disposed over the sensor element. Withreference to FIG. 7, a first embodiment of the sensor device 790includes a sensor element 711 and an optical filter 700 disposed on thesensor element 711. For example, the sensor device 790 may be an ambientlight sensor, the sensor element 711 may be a photodiode, and theoptical filter 700 may be a photopic filter, such as the exemplaryphotopic filter of FIG. 4D, or an IR-blocking filter.

In other embodiments, the sensor device includes a plurality of sensorelements, and a plurality of optical filters disposed over the pluralityof sensor elements. Typically, the sensor elements are disposed in anarray. In other words, the sensor elements form a sensor array, such asa photodiode array, a CCD array, a CMOS array, or any other type ofconventional sensor array. Also typically, the optical filters aredisposed in an array. In other words, the optical filters form anoptical filter array, such as a color filter array (CFA). Preferably,the sensor array and the optical filter array are correspondingtwo-dimensional arrays, i.e., mosaics. For example, the arrays may berectangular arrays having rows and columns.

Usually, the optical filters are substantially separate from oneanother. In other words, the peripheries of the optical filters are notusually in contact with one another. However, in some instances, thedielectric layers of the optical filters may unintentionally touch,while the metal layers, particularly, the tapered edges, remain separatefrom one another.

Typically, the plurality of optical filters includes different types ofoptical filters having different passbands from one another. Forexample, the plurality of optical filters may include color filters,such as red, green, blue, cyan, yellow, and/or magenta filters, photopicfilters, IR-blocking filters, or a combination thereof. In someembodiments, the plurality of optical filters includes different typesof color filters, forming a CFA. For example, the plurality of opticalfilters may include red, green, and blue filters, such as the exemplaryred, green, and blue filters of FIGS. 4A to 4C, forming an RGB filterarray, such as a Bayer filter array.

Advantageously, the different types of optical filters may havedifferent numbers of metal layers and/or different thicknesses of themetal layers from one another. In some embodiments, at least two of thedifferent types of optical filters include different numbers of metallayers from one another. In the same or other embodiments, at least twoof the different types of optical filters have different metal-layerthicknesses from one another. For example, the exemplary blue filter ofFIG. 4C has a different number of metal layers from the exemplary redand green filters of FIGS. 4A and 4B. Moreover, all of the exemplaryred, green, and blue filters of FIGS. 4A to 4C have differentmetal-layer thicknesses from one another.

With reference to FIG. 8, a second embodiment of the sensor device 890includes a plurality of sensor elements 811 and a plurality of opticalfilters 800 and 804 disposed on the plurality of sensor elements 811.The plurality of optical filters 800 and 804 includes a first type ofoptical filter 800 having a first passband, and a second type of opticalfilter 804 having a second passband, different from the first passband.For example, the sensor device 890 may be an image sensor, the pluralityof sensor elements 811 may form a CCD array, and the plurality ofoptical filters 800 and 804 may form a Bayer filter array, of which onlya portion of one row is illustrated. The first type of optical filter800 may be a green filter, such as the exemplary green filter of FIG.4B, and the second type of optical filter 804 may be a blue filter, suchas the exemplary blue filter of FIG. 4C.

Of course, numerous other embodiments may be envisaged without departingfrom the spirit and scope of the invention.

I claim:
 1. An optical filter comprising: a plurality of dielectriclayers; a plurality of metal layers stacked in alternation with theplurality of dielectric layers, wherein each of the plurality ofdielectric layers has a tapered edge at a periphery of the opticalfilter, each of the plurality of metal layers is encapsulated by one ormore of the plurality of dielectric layers, and each of the plurality ofmetal layers is separated from a substrate of the optical filter usingat least one of the plurality of dielectric layers; and one or morecorrosion-suppressing layers substantially encapsulating a metal layerof the plurality of metal layers.
 2. The optical filter of claim 1,wherein the optical filter has a substantially flat top and slopedsides.
 3. The optical filter of claim 1, wherein each of the pluralityof metal layers has a tapered edge, at the periphery of the opticalfilter, that is encapsulated by one or more of the plurality ofdielectric layers.
 4. The optical filter of claim 1, where the one ormore corrosion-suppressing layers comprise: a corrosion-suppressinglayer disposed between a dielectric layer, of the plurality ofdielectric layers, and the metal layer.
 5. The optical filter of claim1, wherein each metal layer, of the plurality of metal layers, isencapsulated by the one or more corrosion-suppressing layers.
 6. Theoptical filter of claim 1, further comprising: a dielectric coatingdeposited on the optical filter.
 7. The optical filter of claim 1,wherein the optical filter is disposed on a sensor element.
 8. Theoptical filter of claim 7, wherein the sensor element is one of aplurality of sensor elements, and the optical filter is one of aplurality of optical filters.
 9. The optical filter of claim 8, whereinthe plurality of sensor elements are disposed in a two-dimensionalarray, and the plurality of optical filters are disposed in acorresponding two-dimensional array.
 10. The optical filter of claim 8,wherein the plurality of optical filters includes different types ofoptical filters having different passbands.
 11. The optical filter ofclaim 10, wherein at least two of the different types of optical filtershave at least one of: different quantities of metal layers from oneanother, or different metal-layer thicknesses from one another.
 12. Theoptical filter of claim 1, wherein the metal layer has a differentthickness than at least one other metal layer of the plurality of metallayers.
 13. The optical filter of claim 1, wherein each of the pluralityof metal layers is composed of silver or a silver alloy.
 14. The opticalfilter of claim 1, wherein each of the plurality of dielectric layers iscomposed of a high-index dielectric material.
 15. The optical filter ofclaim 14, wherein the high-index dielectric material isultraviolet-absorbing.
 16. The optical filter of claim 1, wherein theoptical filter is formed by a lift off process.
 17. The optical filterof claim 16, wherein the lift off process includes: applying aphotoresist layer onto the substrate; patterning the photoresist layer;depositing a multilayer stack on the patterned photoresist layer;depositing a multilayer stack on a filter region of the substrate;removing the photoresist layer; and removing the multilayer stackdeposited on the patterned photoresist layer.
 18. The optical filter ofclaim 17, wherein patterning the photoresist layer includes forming anoverhang in the photoresist layer.
 19. The optical filter of claim 17,wherein the lift off process further includes: depositing a dielectriccoating on the optical filter.
 20. The optical filter of claim 1,wherein each of the one or more corrosion-suppressing layers includesZnO.